TUESDAY, Nov. 3, 2015 (HealthDay News) -- Children with autism may have a greater risk of obesity, with weight differences seen as early as preschool, a new study reveals.

"A lot of things are happening for these families when their children are under 5, including going through the process of getting a diagnosis and just managing day-to-day behaviors and juggling their child's education and treatment needs," said study author Alison Presmanes Hill.

"It is possible that the early signs and symptoms of autism are so salient for parents that they could overshadow concerns about weight problems," explained Hill, who is an assistant professor of pediatrics at the Institute on Development and Disability at Oregon Health and Science University in Portland.

Hill's team found that preschoolers and teens with autism were a little more likely than their peers without the developmental disorder to be overweight or obese.

The findings were published in the Nov. 2 online edition of the journal Pediatrics.

For the study, the researchers weighed and measured more than 5,000 children, aged 2 to 17, who had an autism spectrum disorder. Each child's body mass index (BMI) was compared to the expected range for their age and sex. BMI is a ratio of weight to height.

Kids with a BMI at or above the 95th percentile were considered obese, while those at or above the 85th percentile were deemed overweight. Overall, 34 percent of the kids with autism were overweight compared to 32 percent in the general population, and 18 percent of the kids with autism were obese versus 17 percent in the general population.

Differences were more striking in the preschool and teen years. Compared to others their age, 2- to 5-year-olds who had autism were more likely to be obese -- 16 percent versus 10 percent. And teens with autism also had a higher risk of obesity than their peers -- 26 percent versus 20 percent, the study found.

The researchers also collected information on the children's behavior, mental abilities, medications and other medical conditions. As scores on scales of sleep problems and behavioral difficulties went up, the study authors found the risk of obesity went up, too.

"The most striking feature of this study is that differences in unhealthy weight status between typically developing children and children with autism spectrum disorder are apparent as early as preschool age," said Dr. Sonia Monteiro, a developmental pediatrician at Texas Children's Hospital in Houston. Contributing risk factors may include selective eating, decreased engagement in physical activity and use of medications that can lead to weight gain, she said.

Hill pointed out that one possible reason for lower levels of physical activity in younger children is that preschoolers with autism may participate less often in social activities, which at that age often involve energetic play.

"I believe the observation that children and adolescents with (and without) autism have an alarming rate of obesity is well established," Elliott said. "What remains less clear is what, exactly, one can do about weight problems."

It is already difficult to address obesity in children without developmental disabilities, so suggesting calorie restrictions for children with autism will often be unhelpful, he said.

"Some parents find that it is easier to introduce regular exercise into the lives of their autistic children because routines such as daily walks or bike rides tend to be self-sustaining once established," Elliott said. But that may not be enough when some medications, such as atypical antipsychotics, increase weight and promote fat cell growth in the abdominal area.

"If the culprit is medication, how does one balance benefits with risk?" Elliott said.

Parents can also try to reduce the amount of time children with autism spend with media, such as TV, said Jack Dempsey, a pediatric psychologist at Texas Children's Hospital's Autism Center in Houston.

"To reduce their child's risk for obesity, parents should try to set limits regarding consumption of calorie-dense foods and the amount of screen time from an early age," Dempsey said. He also recommended incorporating physical activity into children's daily routine as a family.

"Parents should keep in mind that these strategies are challenging to implement in children with autism spectrum disorders and not be discouraged by setbacks," Dempsey added.

Also important, Hill added, is that parents do not ignore a child's weight even while they are working to address a child's other challenges.

"We hope that our findings encourage health care providers to start thinking about and proactively addressing weight issues early, so that they don't end up on the back burner," Hill said.